Some investors have agreed to a bond swap with Petróleos de Venezuela SA, in a deal that would provide the national oil company with more time to pay off billion of dollars in debt in exchange for paying more money in the future to the current bondholders.

PdVSA, as the state-owned oil giant is known, initially attracted little investor interest for the swap when the company offered an exchange about three weeks ago. But PdVSA last week decided to sweeten the offer, and it has been able to attract more investor interest, analysts say.

With a Thursday deadline for investors to accept the new terms, some analysts are optimistic that enough bondholders will agree to the exchange of as much as $5.325 billion of debt to make a default less likely next year.

Siobhan Morden, head of Latin America fixed-income strategy at Nomura Securities International, said she expects 50% of the outstanding 2017 bonds to be tendered for a swap. But other analysts are worried about whether the deal could garner enough interest as bond prices have rallied sharply in recent days.

Since the sweetened deal for debt due next April and for debt due next November was announced, prices for PdVSA’s April 2017 bonds have rallied 19% to 85.125 cents on the dollar and the November notes have gained 11% to 85.75 cents.

The price rally suggests “there’s appetite for this deal, and the market is trying to say that it’s going to be a success,” Ms. Morden said.

Newfleet Asset Management, which has $11.4 billion of assets under management, will swap some of its PdVSA bonds with the company, said Daniel Senecal, a portfolio manager.

That would provide some short-term relief to PdVSA, which has been struggling to meet its debt obligations during a long period of low oil prices that has hurt its profits and savaged the energy-dependent Venezuelan economy.

But some investors noted that by issuing even more bonds, PdVSA’s bond exchange would make it more difficult for the company to meet its future debt obligations.

The debt swap is “a very short-term oriented transaction,” said Ricardo Adrogué, head of emerging markets debt at Barings, a $275 billion global asset-management firm, which doesn’t have any exposure to PdVSA debt.

While the exchange could enable PdVSA to roll over its debt, “it comes at a very high price of future promises, promises that become even harder to meet in the future,” Mr. Adrogué​said.

In the exchange, PdVSA is offering the investors new bonds maturing in 2020. The debt’s 8.5% coupon would remain the same for the November note and be up from 5.25% for the April note. All bondholders would receive about $1,200 in bonds for every $1,000 in bonds they now own.

PdVSA debt this year has been among the best-performing assets in emerging markets. Its bonds due April 2017 are up 78% year to date, boosted by the recent oil rally and government assurances that it is willing to pay bondholders despite continued economic hardship.

Some bondholders have decided that they are better off getting paid now rather than risking giving back some of those gains by holding the debt for more years.

Yong Zhu, an emerging-market bond manager at DuPont Capital Management, said the firm had decided not to participate in the exchange.

“We don’t know much about the new bond yet, so we’d like to get paid soon,” Mr. Zhu said.